1. Field of the Invention
The present invention is generally in the field of electrical circuits. More specifically, the invention is in the field of voltage controlled oscillators.
2. Related Art
In the field of wireless communication, such as radio frequency (“RF”) communication, voice and data signals are encoded over a carrier signal prior to transmission. Typically, the carrier signal used for RF communications is a sine wave generated by an oscillator. For example, a typical oscillator used to generate a sine wave for RF communication is a voltage controlled oscillator.
A conventional voltage controlled oscillator generally includes a tank circuit for establishing the oscillation frequency of the output signal generated by the voltage controlled oscillator, where the tank circuit includes a combination of inductive and capacitive components. In the conventional voltage controlled oscillator, the capacitive component typically comprises a variable capacitor, which can be adjusted to allow the output of the voltage controlled oscillator to be tuned to a desired oscillation frequency. In the conventional voltage controlled oscillator, a varactor diode, which has a capacitance that varies according to a voltage applied across the varactor diode, is typically used as the variable capacitor.
Thus, in the conventional voltage controlled oscillator, the output of the voltage controlled oscillator can be tuned by varying the voltage applied across the varactor diode.
However, the varactor diode can cause undesirable tuning non-linearity in the voltage controlled oscillator, which increases design constraints on the circuit in which the voltage controlled oscillator is typically used, such as a phase locked loop. Additionally, the varactor diode can reduce the quality factor of the voltage controlled oscillator, which can cause an increase in phase noise of the voltage controlled oscillator in the gigahertz frequency range.
Thus, there is a need in the art for a voltage controlled oscillator having reduced tuning non-linearity and increased quality factor.